1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to techniques for providing a safety mechanism for a blowout preventer.
2. Discussion of the Background
A subsea blowout preventer (“BOP”) stack is used to seal a wellbore during drilling operations, both for safety and environmental reasons. As shown in FIG. 1, a drilling system 10 used for extracting oil and/or gas from under the sea floor may include a lower blowout preventer stack (“lower BOP stack”) 14, which may be rigidly attached to a wellhead 16 upon the sea floor 12, while a Lower Marine Riser Package (“LMRP”) 18 is retrievably disposed upon a distal end of a marine riser 20, extending from a drill ship 22 or any other type of surface drilling platform or vessel. As such, the LMRP 18 may include a stinger 24 at its distal end configured to engage a receptacle 26 located on a proximal end of the lower BOP stack 14.
In typical configurations, the lower BOP stack 14 may be rigidly affixed atop a subsea wellhead and may include (among other devices) a ram-type blowout preventer (BOP) 28 useful in controlling the well as it is drilled and completed. Similarly, the LMRP 18 may be disposed upon a distal end of a long flexible riser 20 that provides a conduit through which drilling tools and fluids may be deployed to and retrieved from the subsea wellbore. Ordinarily, the LMRP 18 may include (among other things) a ram-type blowout preventer at its distal end such that, when desired, ram-type blowout preventers of the LMRP 18 and the lower BOP stack 14 may be closed and the LMRP 18 may be detached from the lower BOP stack 14 and retrieved to the surface, leaving the lower BOP stack 14 atop the wellhead.
During the operation of the lower BOP stack 14 and/or the LMRP 18, various incidents or simply maintenance events may occur that require access to the BOP 28. For this purpose, the well might be shut down and the part necessary to be worked on may be lifted to the vessel 22. If the equipment necessary for repairing the BOP 28 is not available on the vessel 22, the BOP 28 is shipped to dry locations where the equipment is available. As the BOP 28 is connected to other parts of the lower BOP stack 14 and/or the LMRP 18, which parts may be heavy and linked to the BOP in a complicated manner, it is the practice to remove the whole lower BOP stack 14 and/or LMRP 18 and bring it to the surface for repairs or inspection.
Thus, the weight of the entire lower BOP stack may be in the range of millions of kg and a height of the stack may be up to 10 m. Especially when the repair and/or inspection of the lower BOP stack 14 and/or LMRP 18 is performed on the vessel 22, the sea waves may sometimes tilt these devices so violently that maintenance personnel working around the lower BOP stack 14 and/or LMRP 18 may get injured or even lose their lives.
Accordingly, it would be desirable to provide systems that avoid the afore-described problems and drawbacks.